(The appropriate invocation of ps
varies across different platforms, as do the details of what is
shown. This example is from a recent Linux system.) The first
process listed here is the master server process. The command
arguments shown for it are the same ones used when it was
launched. The next five processes are background worker processes
automatically launched by the master process. (The "stats collector" process will not be present if
you have set the system not to start the statistics collector;
likewise the "autovacuum launcher"
process can be disabled.) Each of the remaining processes is a
server process handling one client connection. Each such process
sets its command line display in the form

postgres: userdatabasehostactivity

The user, database, and (client) host items remain the same
for the life of the client connection, but the activity indicator
changes. The activity can be idle (i.e.,
waiting for a client command), idle in
transaction (waiting for client inside a BEGIN block), or a command type name such as
SELECT. Also, waiting is appended if the server process is
presently waiting on a lock held by another session. In the above
example we can infer that process 15606 is waiting for process
15610 to complete its transaction and thereby release some lock.
(Process 15610 must be the blocker, because there is no other
active session. In more complicated cases it would be necessary
to look into the pg_locks system view to determine who is
blocking whom.)

If you have turned off update_process_title
then the activity indicator is not updated; the process title is
set only once when a new process is launched. On some platforms
this saves a measurable amount of per-command overhead; on others
it's insignificant.

Tip:Solaris
requires special handling. You must use /usr/ucb/ps, rather than /bin/ps. You also must use two w flags, not just one. In addition, your
original invocation of the postgres
command must have a shorter ps
status display than that provided by each server process. If
you fail to do all three things, the ps output for each server process will be the
original postgres command line.